1. Field of the Invention
The present invention relates to a machine tool for machining, in particular for turning and milling, a workpiece having a central bore, comprising a tool holder for holding a tool, a work rest for seating the workpiece, a work mounting for holding the workpiece in place and a drive means for rotating the workpiece about a central rotation axis.
In addition, the invention also relates to a further machine tool for machining, in particular for turning and milling, a workpiece having a central rotation axis, comprising a tool holder for holding a tool, a work rest for seating the workpiece, a work mounting for holding the workpiece in place and a drive means for rotating the workpiece about the rotation axis.
Furthermore, the invention relates to corresponding methods for machining, in particular for turning and milling, a workpiece.
The invention relates in particular to a machine tool and a corresponding method for machining workpieces which, when used as intended, are operated at high rotational speeds and which in particular require milling and turning, such as, for example, a turbocharger compressor impeller.
2. Related Prior Art
In a machine tool known to the applicant for machining a turbocharger compressor impeller, a workpiece blank, the outer contours of which are pre-machined, in particular rough-turned, is put onto a work rest. In this case, the bearing surface of this work rest is adapted to the outer contour, resting thereon, of the compressor impeller, such that the underside of the compressor impeller rests on the work rest as fully as possible. To fix the compressor impeller, a screw is passed through a central bore in the compressor impeller, a nut being screwed onto the top end of said screw, as a result of which the compressor impeller is pressed downward toward the work rest and held in place. After that, the workpiece is machined. In the case of a turbocharger compressor impeller the machining mainly involves milling, by means of which the relatively complex outer surfaces are incorporated in the workpiece blank.
Since such a turbocharger compressor impeller is machined at extremely high rotational speeds (up to 200,000 rev/min), it is necessary for the workpiece blank to be arranged as centrally as possible for the machining, that is to say as concentrically as possible to the machining rotation axis about which the workpiece is rotated during the machining. In the case of workpiece blanks having a pre-machined central bore which defines the axis of rotation during the subsequent operation of the workpiece, it is especially necessary for the machining to be carried out centrally to the central bore. In the known machine tool, however, no adequate precision with regard to the central arrangement of the workpiece or of the central bore thereof can be achieved before and during the machining, for which reason it is absolutely necessary for the workpiece to be re-balanced after the machining in order to remove existing unbalance. For such re-balancing, the workpiece has to be clamped in place again in another fixture, a factor which is time-consuming and once again constitutes a source for inaccuracies.